Title : Fabrication of Fe-Cu catalysts on the basis of copper (II) ferrite
This paper describes the results of the investigation on the ability of copper(II) ferrite (CuFe2O4) to reduction in an electrochemical system with the formation of Fe-Cu composites. The effect of a polymer stabilizer (polyvinyl alcohol, PVA) on structural and phase changes in CuFe2O4 during thermal treatment and subsequent electrochemical reduction has been studied. The electrocatalytic properties of Fe-Cu composites have been tested in reactions of electrohydrogenation of p-nitrobenzoic acid (p-NBA) and acetophenone (APh).
Copper(II) ferrite was synthesized by co-precipitation method from aqueous solutions of copper(II) nitrate and ferric(III) chloride (1:2 molar ratio) without and with the addition of polymer via NaOH. The resulting precipitate was filtered and washed with distilled water. Dried CuFe2O4 and CuFe2O4+PVA samples were thermally treated at 500°?, 700°? and 900°? for 2 hours.
According to XRD results, the copper ferrite samples thermally treated at three temperatures have CuFe2O4 crystalline phases with corresponding peaks of high intensity and CuO in a small amount. The electrochemical reduction of these samples is accompanied by the formation of phase constitutions that differ significantly from each other. Thus, in the CuFe2O4 (500°?) sample copper cations are reduced in a larger amount than iron cations, magnetite is formed (with a possible residue of CuFe2O4), and Cu2O crystalline phases appear. In the composition of CuFe2O4 (700°C) sample the ratio of reduced metals is approximately equal with a slight predominance of iron and a sharp decrease in the Fe3O4 content. In the CuFe2O4 (900°C) sample, the amount of electrochemically reduced iron becomes significantly higher than that of copper. It is concluded that the temperature of heat treatment affects the phase constitution of Fe-Cu composites during reduction in the electrochemical system and the relative content of both metals.
Co-precipitation of CuFe2O4 precursors from an aqueous solution of PVA and subsequent thermal treatment of prepared CuFe2O4 samples lead to the formation of composites whose phase constitutions differ from those prepared without a polymer. In all thermally treated CuFe2O4+PVA samples in addition to CuFe2O4 crystalline phases, the reduced metals appear: Cu0(500°C), Fe0 > Cu0(700°C) and Fe0 ≤ Cu0(900°C), which are obviously formed under the action of polymer decomposition products. In the electrochemical system, additional reduction of metal cations occurs in thermally treated CuFe2O4+PVA samples. The amount of reduced metals increases, and compared to the samples synthesized without polymer, their relative content changes: Fe0 < Cu0(500°C), Fe0 ≤ Cu0(700°C) and Fe0 = Cu0(900°C).
The Fe-Cu composites obtained after thermal treatment and electrochemical reduction were used as electrocatalysts in the electrohydrogenation of p-NBA and APh. The experiments were carried out in a diaphragm cell on a copper cathode in the aqueous-alcoholic-alkaline catholyte at a current of 1.5 A and temperature of 30°?, the anode was a Pt-grid. It was established that the all Fe-Cu composites have electrocatalytic activity, increasing the hydrogenation rate and conversion of p-NBA and APh in comparison with their electrochemical reduction on a Cu cathode (without catalyst). Fe-Cu catalysts prepared in this way can be used in various catalytic and electrocatalytic processes.